Circuit Device and Physical Quantity Detection Device

The present application is based on, and claims priority from JP Application Serial Number 2024-160856, filed Sep. 18, 2024, the disclosure of which is hereby incorporated by reference herein in its entirety.

The present disclosure relates to a circuit device and a physical quantity detection device.

For various systems and electronic apparatuses, devices that can detect different physical quantities, such as gyro sensors for detecting angular velocity and acceleration sensors for detecting acceleration, are currently used. For example, JP-A-2008-224230 discloses a detection device that includes an amplifier circuit that amplifies a detection signal from a vibrator; a filter that performs a filtering process on the amplified detection signal; and an analog-to-digital (A/D) converter that sample-holds the processed detection signal, based on a sample hold signal obtained from a drive signal and A/D-converts the sample-held signal. The filter includes a bandpass filter having frequency characteristics of removing frequency components of unnecessary signals but allowing frequency components of a desired signal to pass therethrough. The detection device disclosed by JP-A-2008-224230 can provide an improved signal-to-noise (S/N) ratio because the bandpass filter can remove unnecessary signals at the previous stage of the sample-holding and the A/D conversion.

If the frequency of the drive signal is 50 kHz, for example, the detection signal from the vibrator can be modulated at 50 kHz. In this case, the bandpass filter in the detection device described in JP-A-2008-224230 needs to have a passband with a center frequency of 50 kHz. On the other hand, to satisfy the demand for a further low-noise detection signal, the bandpass filter needs to sufficiently attenuate the signal at 150 kHz so that noise generated by the third-order harmonics contained in the sample-held signal is not folded back into the signal band.

To satisfy the above conditions, the bandpass filter may be formed of an analog high-order circuit. In addition, an adjustment circuit is necessary to compensate for variations in the characteristics of the vibrator. As a result, the overall circuit scale may be disadvantageously large.

An aspect of the present disclosure is a circuit device connected to a physical quantity detection element that has a driver and a detector. The circuit device includes a drive circuit that drives the driver and that generates a periodic signal, based on a signal output from the driver; a detection circuit that generates a physical quantity detection signal related to a physical quantity detected by the detector, based on a signal output from the detector; and a bandpass filter circuit that receives the periodic signal and that outputs a detection signal through a digital process. The detection circuit includes an analog front end that amplifies the signal output from the detector; an analog-to-digital conversion circuit that converts a signal output from the analog front end into a digital signal; and a demodulation circuit that demodulates a physical quantity signal contained in the digital signal output from the analog-to-digital conversion circuit, based on the detection signal. The detection circuit generates the physical quantity detection signal, based on the demodulated physical quantity signal.

Another aspect of the present disclosure is a circuit device connected to a physical quantity detection element that has a driver and a detector. The circuit device includes a drive circuit that drives the driver and that generates a periodic signal, based on a signal output from the driver; a detection circuit that generates a physical quantity detection signal related to a physical quantity detected by the detector, based on a signal output from the detector. The detection circuit includes an analog front end that amplifies the signal output from the detector; an analog-to-digital conversion circuit that converts a signal output from the analog front end into a digital signal; a bandpass filter circuit that receives the digital signal output from the analog-to-digital conversion circuit; and a demodulation circuit that uses the periodic signal as a detection signal to demodulate a physical quantity signal contained in a signal output from the bandpass filter circuit, based on the detection signal. The detection circuit generates the physical quantity detection signal, based on the demodulated physical quantity signal.

A still another aspect of the present disclosure is a physical quantity detection device that includes an aspect of the circuit device and the physical quantity detection element.

Some preferred embodiments of the present disclosure will be described below in detail with reference to the accompanying drawings. It should be noted that the embodiments described below are not intended to unduly limit the contents of the present disclosure described in the claims. In addition, all the configurations described below may not be essential in the present disclosure.

Hereinafter, a physical quantity detection device, called an angular velocity detection device, that detects an angular velocity as a physical quantity will be described below as an example.

1 FIG. 1 FIG. 1 100 200 100 200 100 200 is a functional block diagram of a physical quantity detection device according to the first embodiment. As illustrated in, a physical quantity detection devicein the first embodiment includes a physical quantity detection elementthat detects a physical quantity; and a circuit deviceconnected to the physical quantity detection element. The circuit deviceis implemented, for example, on a single integrated circuit (IC) chip. Both the physical quantity detection elementand the circuit deviceare mounted in a package (not illustrated), such as a ceramic package.

200 1 2 1 2 100 5 200 The circuit deviceincludes terminals DS, DG, S, S, SS, SCK, SI, and SO as external connection terminals. The terminals DS, DG, S, and Sare electrically connected to the physical quantity detection element. The terminals SS, SCK, SI, and SO are electrically connected to an MCU, which is an external device of the circuit device. The MCU is an abbreviation of a micro control unit.

100 100 The physical quantity detection elementhas a resonator element in which drive electrodes and detection electrodes are disposed. The resonator elements are typically encapsulated in a package with the airtightness thereof secured, so that it is possible to minimize the impedance of the resonator element and increase the oscillation efficiency. In the present embodiment, the physical quantity detection elementincludes, as the resonator element, a so-called double T-shaped resonator element having two T-shaped drive vibration arms.

2 FIG. 2 FIG. 100 100 100 2 is a plan view of the resonator element of the physical quantity detection element. The resonator element of the physical quantity detection elementmay be made of quartz crystal (SiO). Such a quartz crystal resonator element advantageously provides greatly precise detection of angular velocity because the resonance frequency thereof does not largely vary with temperature. The physical quantity detection elementhas, for example, a double T-shaped quartz crystal resonator element formed of a Z-cut quartz crystal substrate. It should be noted that the X-axis, the Y-axis, and the Z-axis inindicate the respective axes of the quartz crystal.

2 FIG. 100 100 100 105 105 100 100 100 107 102 107 100 104 107 105 101 104 104 107 105 101 104 a b a b b a b a a a a a b b b b. As illustrated in, the physical quantity detection elementincludes drivers, a detector, and a plurality of connection arms, or connection armsand, by which the detectoris connected to both the drivers. The detectorincludes a detection base; and a plurality of detection vibration armsextending from the detection base. Of the drivers, a first one includes a drive baseconnected to the detection basevia the connection arm; and a plurality of drive vibration armsextending from the drive base, and a second one includes a drive baseconnected to the detection basevia the connection arm; and a plurality of drive vibration armsextending from the drive base

100 101 104 101 104 112 113 101 113 112 101 112 113 200 a a b b a b 1 FIG. More specifically, in the resonator element of the physical quantity detection element, the drive vibration armsextend from the drive base, respectively, in the ±Y-axial directions, and the drive vibration armsextend from the drive base, respectively, in the ±Y-axial directions. Drive electrodesandare formed, respectively, on the upper and side surfaces of each drive vibration arm; other drive electrodesandare formed, respectively, on the upper and side surfaces of each drive vibration arm. The drive electrodesandare connected, respectively, to the terminal DG and the terminal DS of the circuit deviceillustrated in.

104 107 105 104 107 105 a a b b The drive baseis connected to the detection basehaving a rectangular shape via the connection armextending in the −X-axial direction; the drive baseis connected to the detection basevia the connection armextending in the +X-axial direction.

102 107 114 115 102 116 102 114 115 1 2 200 116 1 FIG. The detection vibration armsextend from the detection base, respectively, in the ±Y-axial directions. Detection electrodesandare formed on the upper surfaces of the detection vibration arms; common electrodesare formed on the side surfaces of the detection vibration arms. The detection electrodesandare connected, respectively, to the terminal Sand terminal Sof the circuit deviceillustrated in. The common electrodesare grounded.

112 113 101 101 101 101 101 101 101 101 a b a b a b a b. 3 FIG. When an alternating current (AC) voltage is applied, as a drive signal, between the drive electrodesandof the drive vibration armsand, as illustrated in, the inverse piezoelectric effect occurs therebetween, thereby causing the drive vibration armsandto perform flexural vibrations with the ends of the two drive vibration armsandrepeatedly moving close to and away from each other, as indicated by arrows B. In this case, the frequency of the flexural vibrations substantially coincides with the resonance frequency of each of the drive vibration armsand

100 101 101 105 105 105 105 102 101 101 102 101 101 a b a b a b a b a b 4 FIG. In the above state, when an angular velocity around the Z-axis, or the rotational axis, is applied to the resonator element of the physical quantity detection element, each of the drive vibration armsandis given a Coriolis force in a direction perpendicular to the Z-axis and the directions of the flexural vibrations indicated by arrows B. As a result, as illustrated in, each of the connection armsandvibrates as indicated by arrows C. In conjunction with the vibrations of the connection armsand, each detection vibration armperforms a flexural vibration, as indicated by arrows D. The frequency of the flexural vibrations coincides with the frequency of the flexural vibration of each of the drive vibration armsand. The phase of the flexural vibration of each of the detection vibration armsinvolved in the Coriolis force is shifted by 90° from the phase of the flexural vibration of each of the drive vibration armsandinvolved in the Coriolis force.

114 115 102 100 Because of the piezoelectric effect, AC charges based on these flexural vibrations are generated in the detection electrodesandof the detection vibration arms. In this case, the AC charges generated based on the Coriolis force change in accordance with the magnitude of the Coriolis force, namely, the magnitude of the angular velocity applied to the physical quantity detection element.

103 101 101 101 101 103 101 101 106 102 102 106 102 114 115 a b a b a b A weight section, which is wider than any of the drive vibration armsand, is formed at the end of each of the drive vibration armsand. By forming the weight sectionat the end of each of the drive vibration armsand, a large amount of Coriolis force is generated, so that a desired resonance frequency can be obtained from the relatively short vibrating arms. Similarly, a weight section, which is wider than the detection vibration arms, is formed at the end of each detection vibration arm. By forming the weight sectionat the end of each detection vibration arm, larger amounts of AC charges can be generated in the detection electrodesand.

100 114 115 As described above, the physical quantity detection elementoutputs, via the detection electrodesand, an angular velocity signal, which is the AC charge based on the Coriolis force around the Z-axis, or the detection axis.

1 FIG. 200 10 20 30 40 50 60 200 Returning to the explanation with reference to, the circuit deviceincludes a drive circuit, a detection circuit, a bandpass filter (BPF) circuit, an oscillation circuit, an interface (I/F) circuit, and a storage. In the circuit device, some of these components may be removed or replaced. Alternatively, some other elements may be added thereto.

10 100 100 100 10 113 100 100 10 112 100 10 30 10 a a The drive circuitdrives the driversof the physical quantity detection elementand generates a periodic signal SX based on a signal output from the drivers. More specifically, the drive circuitapplies a drive signal DRV to the drive electrodesof the physical quantity detection elementvia the terminal DS, thereby exciting and vibrating the physical quantity detection elementin accordance with the drive signal DRV. The drive circuitis then supplied, via the terminal DG, with an oscillation current generated in each drive electrodein response to the excitation vibration of the physical quantity detection elementand performs feedback control of the amplitude level of the drive signal DRV such that the amplitude of the oscillation current is kept constant. The drive circuitthen generates the periodic signal SX having the same phase as the drive signal DRV and outputs the periodic signal SX to the BPF circuit. Details of the operation of the drive circuitwill be described later.

30 30 30 The BPF circuitis a digital filter that receives the periodic signal SX and outputs a detection signal SDT through a digital process. The periodic signal SX, which is a rectangular wave signal, contains odd-order harmonics together with a fundamental mode thereof. The BPF circuitwhose center frequency is tuned to the frequency of the fundamental mode of the periodic signal SX allows the fundamental mode to pass therethrough while sufficiently attenuating the odd-order harmonics. If the frequency of the fundamental mode is 50 kHz, for example, the frequency of the third-order harmonics is 150 kHz, in which case the BPF circuitserves as a digital filter whose passband contains 50 kHz and cutoff frequency is lower than 150 kHz on the high-frequency side.

20 100 100 100 20 114 115 100 50 b b The detection circuitgenerates an angular velocity detection signal SDO related to the angular velocity detected by the detector, based on a signal output from the detectorof the physical quantity detection element. More specifically, the detection circuitgenerates a digital signal, or the angular velocity detection signal SDO, based on the signals output from the respective detection electrodesandof the physical quantity detection elementand then outputs the generated angular velocity detection signal SDO to the I/F circuit.

1 FIG. 20 21 22 23 24 As illustrated in, the detection circuitincludes an analog front end (AFE), an A/D conversion circuit (ADC), a demodulation circuit, and a correction circuit.

21 100 100 21 114 115 100 b The AFEamplifies the signals output from the detectorof the physical quantity detection element. More specifically, the AFEdifferentially amplifies the two signals output from the detection electrodesandof the physical quantity detection elementand then outputs an analog signal, or an amplified signal SAO.

22 21 22 The ADC circuitconverts the amplified signal SAO output from the AFEinto a digital signal ADO. The ADC circuitmay be a delta-sigma A/D conversion circuit that outputs a 1-bit digital signal ADO. Because of the noise-shaping effect thereof, the delta-sigma A/D conversion circuit reduces noise contained in the digital signal ADO within the signal band.

23 22 30 23 22 The demodulation circuitdemodulates an angular velocity signal AVO, which is a physical quantity signal contained in the digital signal ADO output from the ADC circuit, based on the detection signal SDT output from the BPF circuit. In the present embodiment, the demodulation circuituses the digital signal ADO output from the ADC circuitas a detected signal to mix the digital signal ADO, which is the detected signal, with the detection signal SDT, thereby demodulating the angular velocity signal AVO.

24 24 20 50 The correction circuitsubjects the angular velocity signal AVO to various types of correction processes, such as a low-pass filter process, an offset correction, a temperature correction, and a sensitivity correction. The signal obtained through the process of the correction circuitis output from the detection circuitto the I/F circuitas the angular velocity detection signal SDO, which is a physical quantity detection signal.

20 23 20 5 50 5 In the above way, the detection circuitgenerates the angular velocity detection signal SDO, based on the angular velocity signal AVO demodulated by the demodulation circuit. Alternatively, without performing any process, the detection circuitmay output the angular velocity signal AVO as the angular velocity detection signal SDO to the MCUvia the I/F circuit, and the MCUmay perform a low pass filter process or various correction processes on the angular velocity detection signal SDO.

30 23 24 30 23 24 Each of the BPF circuit, the demodulation circuit, and the correction circuitis a digital circuit and operates in synchronization with a master clock signal MCLK. At least some of the functions of the BPF circuit, the demodulation circuit, and the correction circuitmay be implemented by a DSP. The DSP is an abbreviation for a digital signal processor.

60 10 20 60 200 10 20 The storagehas a nonvolatile memory (not illustrated), which stores various pieces of trimming data to be used by the drive circuitand the detection circuit. The nonvolatile memory may be a MONOS memory or an EEPROM, for example. The MONOS is an abbreviation for metal oxide nitride oxide silicon. The EEPROM is an abbreviation of electrically erasable programmable read-only memory. Furthermore, the storagehas a register (not illustrated). When the circuit deviceis turned on, namely, when the voltage at a terminal VDD rises from 0 V to a desired value, various pieces of trimming data that have been stored in the nonvolatile memory may be transferred to the register and retained therein. Then, the trimming data that have been retained in the register may be supplied to the drive circuitor the detection circuit.

40 22 23 24 30 40 The oscillation circuitgenerates the master clock signal MCLK and then supplies the master clock signal MCLK to the ADC circuit, the demodulation circuit, the correction circuit, and the BPF circuit. The oscillation circuitmay generate the master clock signal MCLK by using, for example, a ring oscillator or a CR oscillation circuit.

5 200 50 20 5 In response to a request from the MCU, which is an external device of the circuit device, the I/F circuitperforms a process of outputting the angular velocity detection signal SDO output from the detection circuitto the MCU.

5 50 60 5 5 60 In response to another request from the MCU, the I/F circuitperforms a process of reading data stored in the nonvolatile memory and the registers of the storageand outputting the data to the MCUor a process of writing data input from the MCUto the nonvolatile memory and the registers of the storage.

50 5 200 5 200 50 2 2 The I/F circuit, which is an interface circuit of an SPI bus, for example, receives a selection signal, a clock signal, and a data signal transmitted from the MCU, respectively, via the terminals SS, SCK, and SI of the circuit deviceand, in turn, outputs a data signal to the MCUvia the terminal SO of the circuit device. The SPI is an abbreviation for serial peripheral interface. In this case, the I/F circuitmay be an interface circuit that supports various buses, including an IC bus, for example, other than the SPI bus. The IC is an abbreviation for inter-integrated circuit.

5 FIG. 5 FIG. 10 10 11 12 13 14 15 is a diagram of an example of a configuration of the drive circuit. As illustrated in, the drive circuitincludes an I/V conversion circuit, a full-wave rectifier circuit, an automatic gain control (AGC) circuit, a drive signal generation circuit, and a buffer circuit.

100 112 11 11 11 12 14 15 When the physical quantity detection elementis excited and vibrates to generate an oscillation current through the drive electrodes, this oscillation current is supplied to the I/V conversion circuitvia the terminal DG and is then converted into an AC voltage signal IVO by the I/V conversion circuit. The AC voltage signal IVO output from the I/V conversion circuitenters the full-wave rectifier circuit, the drive signal generation circuit, and the buffer circuit.

12 11 The full-wave rectifier circuitperforms full-wave rectification on the AC voltage signal IVO output from the I/V conversion circuitand then outputs a direct current (DC) signal.

13 12 13 12 The AGC circuitamplifies the signal output from the full-wave rectifier circuitand then outputs a signal having a predetermined voltage. The AGC circuitcontrols the amplification gain in accordance with the magnitude of the signal output from the full-wave rectifier circuitsuch that the output signal is kept at a predetermined voltage.

14 13 113 100 100 101 101 100 a b The drive signal generation circuitbinarizes the AC voltage signal IVO to generate the drive signal DRV and then outputs the drive signal DRV. The high-level voltage of the drive signal DRV corresponds to the voltage of the signal output from the AGC circuitand is kept at the predetermined voltage. The drive signal DRV is supplied to each drive electrodeof the physical quantity detection elementvia the terminal DS. By receiving the drive signal DRV, the physical quantity detection elementcan continue the excitation and the vibration. Furthermore, since the high-level voltage of the drive signal DRV is kept constant, the drive vibration armsandof the physical quantity detection elementcan vibrate at a constant speed. Therefore, the vibration speed, which is the cause of generating the Coriolis force, can be made more constant to provide stabler sensitivity.

15 30 11 15 The buffer circuitreceives the AC voltage signal IVO and then outputs the periodic signal SX, which is a rectangular wave signal having the same phase as the AC voltage signal IVO. The periodic signal SX is supplied to the BPF circuit. In this case, a filter may be provided between the output of the I/V conversion circuitand the input of the buffer circuit.

6 FIG. 6 FIG. 21 23 21 211 212 213 is a diagram of an example of a configuration of the AFEand the demodulation circuit. As illustrated in, the AFEincludes Q/V conversion circuitsandand a differential amplification circuit.

211 1 114 100 212 2 115 100 The Q/V conversion circuitis supplied with, via the terminal S, an AC charge generated through the detection electrodeof the physical quantity detection element. The Q/V conversion circuitis supplied with, via the terminal S, an AC charge generated through the detection electrodeof the physical quantity detection element.

2 FIG. 100 102 114 102 115 114 115 100 In the present embodiment, as illustrated in, when an angular velocity is applied to the physical quantity detection element, the detection vibration armon which the detection electrodeis formed and the detection vibration armon which the detection electrodeis formed perform flexural vibrations in mutually opposite directions so as to be kept in balance. For this reason, the angular velocity signal contained in the AC charge generated in the detection electrodeand the angular velocity signal contained in the AC charge generated in the detection electrodehave mutually opposite phases. Herein, cases where two angular velocity signals have mutually opposite phases include a case where the difference in phase between the two angular velocity signals is exactly 180° as well as a case where the difference in phase between the two angular velocity signals slightly deviates from 180°, for example, due to an error caused during the manufacturing of the physical quantity detection elementand an error involved in the delay time of the signal propagation path.

211 114 100 1 1 212 115 100 2 2 The Q/V conversion circuitconverts the AC charge supplied through the detection electrodeof the physical quantity detection elementinto an AC voltage signal SO and then outputs the AC voltage signal SO. Likewise, the Q/V conversion circuitconverts the AC charge supplied through the detection electrodeof the physical quantity detection elementinto an AC voltage signal SO and then outputs the AC voltage signal SO.

213 1 211 2 212 1 2 The differential amplification circuitreceives a differential signal pair formed of both the AC voltage signal SO output from the Q/V conversion circuitand the AC voltage signal SO output from the Q/V conversion circuit, then amplifies the difference between the AC voltage signal SO and the AC voltage signal SO, and outputs an amplified signal SAO. The angular velocity signal contained in the amplified signal SAO has substantially the same phase as the drive signal DRV and is a signal modulated at, for example, several tens of kHz, which corresponds to the frequency of the drive signal DRV.

22 22 21 23 22 The amplified signal SAO enters the ADC circuit. As described above, the ADC circuitconverts the amplified signal SAO output from the AFEinto the digital signal ADO and then outputs the digital signal ADO to the demodulation circuit. For example, the ADC circuitis a delta-sigma A/D conversion circuit that operates in synchronization with the master clock signal MCLK and outputs a 1-bit digital signal ADO. For example, the frequency of the master clock signal MCLK is several tens of MHz. Because of the noise-shaping effect thereof, the delta-sigma A/D conversion circuit provides the digital signal ADO in which noise contained within a signal band of, for example, several tens of kHz has been effectively reduced.

23 231 231 22 30 231 231 The demodulation circuitincludes a mixing circuit. The mixing circuituses the digital signal ADO output from the ADC circuitas the detected signal to mix the digital signal ADO, which is the detected signal, with the detection signal SDT output from the BPF circuit. In short, the mixing circuitoutputs a digital signal obtained by multiplying the digital signal ADO by the detection signal SDT. If the digital signal ADO is a 1-bit digital signal and the detection signal SDT is a 16-bit digital signal, for example, the mixing circuitoutputs a 16-bit digital signal, which becomes 0 when the value of the digital signal ADO is 0 and becomes the digital value of the detection signal SDT when the value of the digital signal ADO is 1.

231 23 24 The angular velocity signal contained in the digital signal ADO has substantially the same phase as the periodic signal SX. Since the phase of the detection signal SDT is substantially the same as the phase of the periodic signal SX, the phase of the angular velocity signal contained in the digital signal ADO is substantially the same as the phase of the detection signal SDT. Therefore, the mixing circuitdemodulates the angular velocity signal contained in the digital signal ADO and then outputs an output signal as the angular velocity signal AVO from the demodulation circuitto the correction circuit.

30 30 231 30 30 As described above, the BPF circuitis a digital filter that receives the periodic signal SX and outputs a digital signal obtained by sufficiently attenuating harmonics contained in the periodic signal SX. Using the digital signal output from the BPF circuitas the detection signal SDT as in the present embodiment, the mixing circuitcan reduce harmonic noise within the frequency band which is to be folded back into the signal band, so that it is possible to demodulate the angular velocity signal AVO with great precision. Furthermore, being formed as a digital circuit, the BPF circuitdoes not involve a large circuit area and a large amount of power consumption, compared to a case where the BPF circuitis formed as an analog circuit.

1 200 30 23 30 30 1 200 According to a physical quantity detection devicein the first embodiment, a circuit deviceincludes a BPF circuitthat outputs a detection signal SDT obtained by sufficiently attenuating harmonics contained in a periodic signal SX. Thus, when demodulating an angular velocity signal AVO based on the detection signal SDT, a demodulation circuitcan suppress high-frequency noise generated by harmonics contained in the detection signal SDT from being folded back into the signal band. Furthermore, being formed as a digital circuit, the BPF circuitdoes not involve a large circuit area and a large amount of power consumption, compared to a case where the BPF circuitis formed as an analog circuit. Therefore, the physical quantity detection devicein the first embodiment can provide a low-noise physical quantity detection signal with a small scale of circuitry in circuit device.

1 200 1 200 According to the physical quantity detection devicein the first embodiment, using a digital circuit to perform a bandpass filter process and a process of demodulating the angular velocity signal AVO, the circuit devicecan reduce low-frequency noise, such as 1/f noise, generated in the angular velocity detection signal SDO within the signal band, compared to the related art in which an analog circuit performs a bandpass filter process or a demodulation process. Therefore, with the physical quantity detection devicein the first embodiment, the circuit devicecan provide a low-noise angular velocity detection signal SDO.

1 22 200 22 231 23 200 According to the physical quantity detection devicein the first embodiment, being formed as a delta-sigma A/D conversion circuit, an ADC circuitin the circuit devicereduces noise contained in a digital signal ADO within the signal band, because of the noise-shaping effect of the delta-sigma A/D conversion circuit. Moreover, being formed as a delta-sigma A/D conversion circuit, the ADC circuitgenerates a 1-bit digital signal ADO. Therefore, a mixing circuitincluded in the demodulation circuitcan be implemented in a simple configuration so that a compact circuit devicecan be realized.

Hereinafter, components in a second embodiment which are similar to those in the foregoing first embodiment are denoted by the same reference numerals. In addition, the components that have already been described in the first embodiment will not be described or will be described briefly. Thus, the description will be mainly focused on components different from those in the first embodiment.

7 FIG. 7 FIG. 1 1 100 200 100 is a functional block diagram of a physical quantity detection deviceaccording to the second embodiment. As illustrated in, the physical quantity detection devicein the second embodiment includes a physical quantity detection elementand a circuit device. Since the configuration of the physical quantity detection elementis the same as in the first embodiment, the description thereof will not be given.

200 10 20 40 50 60 200 The circuit deviceincludes a drive circuit, a detection circuit, an oscillation circuit, an interface (I/F) circuit, and a storage. In the circuit device, some of these components may be removed or replaced. Alternatively, some other elements may be added thereto.

10 100 100 100 10 23 20 a a Similar to the first embodiment, the drive circuitdrives driversof the physical quantity detection elementand generates a periodic signal SX based on a signal output from the drivers. In the second embodiment, the drive circuitoutputs the generated periodic signal SX to a demodulation circuitin the detection circuit.

20 100 100 100 20 21 22 23 24 25 b b 7 FIG. Similar to the first embodiment, the detection circuitgenerates an angular velocity detection signal SDO related to the angular velocity detected by a detectorof the physical quantity detection element, based on a signal output from the detector. Similar to the first embodiment, as illustrated in, the detection circuitincludes an analog front end (AFE), an A/D conversion (ADC) circuit, the demodulation circuit, and a correction circuitand further includes a bandpass filter (BPF) circuit.

21 100 100 21 114 115 100 b The AFEamplifies the signals output from the detectorof the physical quantity detection element. More specifically, the AFEdifferentially amplifies the two signals output from the detection electrodesandof the physical quantity detection elementand then outputs an analog signal, or an amplified signal SAO.

22 21 22 The ADC circuitconverts the amplified signal SAO output from the AFEinto a digital signal ADO. The ADC circuitmay be a delta-sigma A/D conversion circuit that outputs a 1-bit digital signal ADO. Because of the noise-shaping effect thereof, the delta-sigma A/D conversion circuit reduces noise contained in the digital signal ADO within the signal band.

25 22 100 100 25 25 b The BPF circuitis a digital filter that receives the digital signal ADO output from the ADC circuitand then outputs a digital signal BPO through a digital process. Since the signals output from the detectorof the physical quantity detection elementare modulated at the frequency of a drive signal DRV, the digital signal ADO is also modulated at that frequency. Since the frequency of the periodic signal SX coincides with the frequency of the drive signal DRV, the BPF circuithas a passband whose center frequency is tuned to the frequency of the fundamental mode of the periodic signal SX and which sufficiently attenuates noise of frequencies that are odd multiples of the center frequency. If the frequency of the fundamental mode of the periodic signal SX is 50 kHz, for example, the BPF circuitserves as a digital filter that has a passband containing 50 kHz and a cutoff frequency lower than 150 kHz on the high-frequency side.

23 10 25 23 25 The demodulation circuituses the periodic signal SX output from the drive circuitas a detection signal to demodulate an angular velocity signal AVO, which is a physical quantity signal contained in the digital signal BPO output from the BPF circuit, based on the periodic signal SX, which is a detection signal. In the present embodiment, the demodulation circuituses the digital signal BPO output from the BPF circuitas a detected signal to mix the digital signal BPO, which is the detected signal, with the periodic signal SX, which is the detection signal, thereby demodulating the angular velocity signal AVO.

24 24 20 50 The correction circuitsubjects the angular velocity signal AVO to various types of correction processes, such as a low-pass filter process, an offset correction, a temperature correction, and a sensitivity correction. The signal obtained through the process of the correction circuitis output from the detection circuitto the I/F circuitas the angular velocity detection signal SDO, which is a physical quantity detection signal.

20 23 20 5 50 5 In the above way, the detection circuitgenerates the angular velocity detection signal SDO, based on the angular velocity signal AVO demodulated by the demodulation circuit. Alternatively, without performing any process, the detection circuitmay output the angular velocity signal AVO as the angular velocity detection signal SDO to the MCUvia the I/F circuit, and the MCUmay perform a low pass filter process or various correction processes on the angular velocity detection signal SDO.

40 50 60 Since the configurations and processes of the oscillation circuit, the I/F circuit, and the storageare the same as in the first embodiment, the description thereof will not be given.

8 FIG. 8 FIG. 21 23 21 211 212 213 is a diagram of an example of a configuration of the AFEand the demodulation circuit. As illustrated in, the AFEincludes Q/V conversion circuitsandand a differential amplification circuit, similar to the first embodiment.

211 1 114 100 211 1 1 212 2 115 100 212 2 2 The Q/V conversion circuitis supplied with, via the terminal S, an AC charge generated through the detection electrodeof the physical quantity detection element. Then, the Q/V conversion circuitconverts the AC charge into an AC voltage signal SO and outputs the AC voltage signal SO. The Q/V conversion circuitis supplied with, via the terminal S, an AC charge generated through the detection electrodeof the physical quantity detection element. Then, the Q/V conversion circuitconverts the AC charge into an AC voltage signal SO and outputs the AC voltage signal SO.

213 1 211 2 212 1 2 The differential amplification circuitreceives a differential signal pair formed of both the AC voltage signal SO output from the Q/V conversion circuitand the AC voltage signal SO output from the Q/V conversion circuit, then amplifies the difference between the AC voltage signal SO and the AC voltage signal SO, and outputs an amplified signal SAO.

22 21 25 As described above, the ADC circuitconverts the amplified signal SAO output from the AFEinto the digital signal ADO and outputs the digital signal ADO to the BPF circuit.

25 22 As described above, the BPF circuitreceives the digital signal ADO output from the ADC circuitand outputs the digital signal BPO.

23 231 231 25 231 231 The demodulation circuitincludes a mixing circuit. The mixing circuituses the digital signal BPO output from the BPF circuitas the detected signal to mix the digital signal BPO, which is the detected signal, with the periodic signal SX, which is the detection signal. In short, the mixing circuitoutputs a digital signal obtained by multiplying the digital signal BPO by the periodic signal SX. If the digital signal BPO is a 16-bit digital signal and the periodic signal SX is a 1-bit digital signal, for example, the mixing circuitoutputs a 16-bit digital signal, which becomes 0 when the value of the periodic signal SX is 0 and becomes the digital value of the digital signal BPO when the value of the periodic signal SX is 1.

231 23 24 The angular velocity signal contained in the digital signal BPO has substantially the same phase as the periodic signal SX. Therefore, the mixing circuitdemodulates the angular velocity signal contained in the digital signal BPO and then outputs an output signal as the angular velocity signal AVO from the demodulation circuitto the correction circuit.

25 231 As described above, the BPF circuitis a digital filter that receives the digital signal ADO and then outputs the digital signal BPO obtained by reducing, contained in the digital signal ADO, noise whose frequencies are odd multiples of the frequency of the fundamental mode of the periodic signal SX. Therefore, using the digital signal BPO as the detected signal as in the present embodiment, the mixing circuitremoves almost all noise within the frequency bands which are odd-order harmonics of the periodic signal SX and which is to be folded back into the signal band. It is thereby possible to demodulate the angular velocity signal AVO with great precision.

1 Other configurations of the physical quantity detection devicein the second embodiment are the same as in the first embodiment, and descriptions thereof will not be given accordingly.

1 200 25 22 23 25 25 1 200 1 1 According to a physical quantity detection devicein the second embodiment, a circuit deviceincludes a BPF circuitthat outputs a signal obtained by sufficiently attenuating high-frequency noise contained in a digital signal ADO output from the ADC circuit. Thus, when demodulating an angular velocity signal AVO based on a detection signal SDT, a demodulation circuitcan suppress high-frequency noise generated by harmonics contained in the detection signal SDT from being folded back into the signal band. Furthermore, being formed as a digital circuit, the BPF circuitdoes not involve a large circuit area and a large amount of power consumption, compared to a case where the BPF circuitis formed as an analog circuit. Therefore, the physical quantity detection devicein the second embodiment can provide a low-noise physical quantity detection signal with a small scale of circuitry in circuit device. Other effects of the physical quantity detection devicein the second embodiment are the same as those of the physical quantity detection devicein the first embodiment.

Hereinafter, components in a third embodiment which are similar to those in the foregoing first embodiment are denoted by the same reference numerals. In addition, the components that have already been described in the first embodiment will not be described or will be described briefly. Thus, the description will be mainly focused on components different from those in the first embodiment.

9 FIG. 9 FIG. 1 1 100 200 100 is a functional block diagram of a physical quantity detection deviceaccording to the third embodiment. As illustrated in, the physical quantity detection devicein the third embodiment includes a physical quantity detection elementand a circuit device. Since the configuration of the physical quantity detection elementis the same as in the first embodiment, the description thereof will not be given.

200 10 20 30 40 50 60 70 200 10 20 40 50 60 Similar to the first embodiment, the circuit deviceincludes a drive circuit, a detection circuit, a bandpass filter (BPF) circuit, an oscillation circuit, an interface (I/F) circuit, and a storageand further includes a center frequency control circuit. In the circuit device, some of these components may be removed or replaced. Alternatively, some other elements may be added thereto. Since the configurations and processes of the drive circuit, the detection circuit, the oscillation circuit, the I/F circuit, and the storageare the same as those in the first embodiment, the descriptions thereof will not be given.

30 30 30 70 30 70 30 70 30 30 30 The BPF circuitoperates in synchronization with a master clock signal MCLK. Therefore, when the frequency of the master clock signal MCLK is shifted from a target frequency, the center frequency of the BPF circuitdoes not coincide with the frequency of a periodic signal SX, in which case the BPF circuitmay fail to sufficiently reduce some harmonics contained in a periodic signal SX. In the present embodiment, the center frequency control circuitthus controls the center frequency of the BPF circuit, based on the difference in phase between the periodic signal SX and a detection signal SDT. More specifically, when the phase of the detection signal SDT is later than the phase of the periodic signal SX, the center frequency control circuitincreases the center frequency of the BPF circuit. When the phase of the detection signal SDT is earlier than the phase of the periodic signal SX, the center frequency control circuitdecreases the center frequency of the BPF circuit. In this way, the control is performed such that the center frequency of the BPF circuitcoincides with the frequency of the periodic signal SX. As a result, the BPF circuitcan sufficiently reduce harmonics contained in the periodic signal SX, thereby providing the detection signal SDT closer to a sine wave.

30 231 Using a digital signal output from the BPF circuitas the detection signal SDT, a mixing circuitremoves almost all noise within the frequency bands of harmonics to be folded back into the signal band. It is thereby possible to demodulate the angular velocity signal AVO with great precision.

1 Other configurations of the physical quantity detection devicein the third embodiment are the same as in the first embodiment, and descriptions thereof will not be given accordingly.

1 100 100 30 200 1 23 200 a According to a physical quantity detection devicein the third embodiment described above, even if a periodic signal SX based on a signal output from driversof a physical quantity detection elementis asynchronous to a master clock signal MCLK used for a BPF circuitto generate a detection signal SDT, a circuit deviceprovides a detection signal SDT that is synchronized with the periodic signal SX. Therefore, the physical quantity detection devicein the third embodiment can accurately detect an angular velocity because the demodulation circuitin the circuit devicedemodulates an angular velocity signal AVO with great precision.

The present disclosure is not limited to the foregoing embodiments and can undergo various modifications within the scope of the spirit of the present disclosure.

1 30 10 1 25 22 1 30 10 25 22 23 For example, the physical quantity detection devicein the foregoing first embodiment or third embodiment is provided with the BPF circuitat the subsequent stage of the drive circuit. In addition, the physical quantity detection devicein the foregoing second embodiment is provided with the BPF circuitat the subsequent stage of an ADC circuit. However, the physical quantity detection devicemay be provided with both the BPF circuitat the subsequent stage of the drive circuitand the BPF circuitat the subsequent stage of the ADC circuit. With this, the demodulation circuitcan demodulate an angular velocity signal AVO with greater precision.

200 200 1 200 6 6 6 200 22 23 24 30 1 22 23 24 30 10 FIG. For example, in each of the foregoing embodiments, the master clock signal MCLK is generated inside a circuit device; however, the master clock signal MCLK may be supplied from the outside of the circuit device. As an example, a physical quantity detection deviceillustrated inincludes a circuit devicethat has, as an external connection terminal, a terminal EXCK at which a clock signal is to be supplied. The terminal EXCK is connected to a temperature compensated crystal oscillator (TCXO). The TCXOoutputs a clock signal whose frequency does not largely fluctuate with temperature. The clock signal output from the TCXOenters the circuit devicevia the terminal EXCK and is then supplied as a master clock signal MCLK to the ADC circuit, the demodulation circuit, the correction circuit, and the BPF circuit. The physical quantity detection devicein the present modification can provide an angular velocity detection signal SDO with great precision because the ADC circuit, the demodulation circuit, the correction circuit, and the BPF circuitall operate in accordance with the master clock signal MCLK having extremely small frequency deviations.

1 100 1 1 In each of the foregoing embodiments, the physical quantity detection deviceincludes a physical quantity detection elementthat detects an angular velocity as a physical quantity; however, the physical quantity detection devicemay include some physical quantity detection elements that detect physical quantities other than an angular velocity. For example, the physical quantity detection devicemay include physical quantity detection elements that detect an acceleration, an angular acceleration, a velocity, a force, and some other physical quantities.

1 1 1 1 1 In each of the above-described embodiments, the physical quantity detection deviceincludes a single physical quantity detection element; however, the physical quantity detection devicemay include a plurality of physical quantity detection elements. As an example, the physical quantity detection devicemay include a plurality of physical quantity detection elements, each of which may detect a physical quantity by using one of two or more mutually orthogonal axes as a detection axis thereof. As another example, the physical quantity detection devicemay include a plurality of physical quantity detection elements, each of which detects one of a plurality of physical quantities including an angular velocity, an acceleration, an angular acceleration, a velocity, and a force. In short, the physical quantity detection devicemay serve as a composite sensor.

100 2 3 3 In each of the foregoing embodiments, as an example, the resonator element of the physical quantity detection elementis a double T-shaped quartz crystal resonator element. However, the resonator element of the physical quantity detection element which detects any given physical quantity may be, for example, of a tuning fork type or a comb tooth type or may be of a vibrating reed type having a triangular prism shape, a quadrangular prism shape, a cylindrical shape, or other shape. Instead of quartz crystal (SiO), the material of the resonator element of the physical quantity detection element may be a piezoelectric material, examples of which include piezoelectric single crystal such as lithium tantalate (LiTaO) or lithium niobate (LiNbO); and piezoelectric ceramic such as lead zirconate titanate (PZT) or may be a silicon semiconductor. Alternatively, the resonator element of the physical quantity detection element may have a structure in which a piezoelectric thin film, which is made of zinc oxide (ZnO), aluminum nitride (AlN), or other material interposed between drive electrodes, is mounted on a portion of a surface of a silicon semiconductor. For example, the physical quantity detection element may be a MEMS element. The MEMS is an abbreviation for micro electromechanical systems.

In addition, in each of the foregoing embodiments, a piezoelectric physical quantity detection element is used as an example; however, a physical quantity detection element which detects any given physical quantity is not limited to such a piezoelectric element. Alternatively, the piezoelectric physical quantity detection element may be an electrostatic capacitance, electrodynamic, eddy current, optical, strain gauge, or other type of element. A detection method employed by a physical quantity detection element is not limited to a method using vibrations; alternatively, the detection method may be, for example, a method using light, rotations, or fluids.

The foregoing embodiments and modifications are merely examples and are not intended to limit the present disclosure. For example, some of the embodiments and the modifications may be combined together as appropriate.

The present disclosure may include a configuration that is substantially equivalent to any of the configurations described in the foregoing embodiments; for example, the present disclosure may include a configuration that provides the same function, method, and result or a configuration that achieves the same object and effect. The present disclosure may include a configuration in which, of components described in the embodiments, non-essential ones are replaced with others. The present disclosure may further include a configuration that can produce the same effects as the configurations described in the embodiments or a configuration that can achieve the same object as the configurations described in the embodiments. The present disclosure may further include a configuration conceived by adding a known technology to the configurations described in the embodiments.

The following aspects are derived from the foregoing embodiments and modifications.

A first aspect of the present disclosure is a circuit device connected to a physical quantity detection element that has a driver and a detector. The circuit device includes a drive circuit that drives the driver and that generates a periodic signal, based on a signal output from the driver; a detection circuit that generates a physical quantity detection signal related to a physical quantity detected by the detector, based on a signal output from the detector; and a bandpass filter circuit that receives the periodic signal and that outputs a detection signal through a digital process. The detection circuit includes an analog front end that amplifies the signal output from the detector; an analog-to-digital conversion circuit that converts a signal output from the analog front end into a digital signal; and a demodulation circuit that demodulates a physical quantity signal contained in the digital signal output from the analog-to-digital conversion circuit, based on the detection signal. The detection circuit generates the physical quantity detection signal, based on the demodulated physical quantity signal.

A circuit device, as described above, includes a bandpass filter circuit that outputs a detection signal obtained by sufficiently attenuating harmonics contained in a periodic signal. Thus, when demodulating a physical quantity signal based on the detection signal, a demodulation circuit can suppress high-frequency noise generated by harmonics contained in the detection signal from being folded back into the signal band. Furthermore, being formed as a digital circuit, the bandpass filter circuit does not involve a large circuit area and a large amount of power consumption, compared to a case where the bandpass filter circuit is formed as an analog circuit. Therefore, this circuit device can provide a low-noise physical quantity detection signal with a small scale of circuitry therein.

Using a digital circuit to perform a bandpass filter process and a process of demodulating the physical quantity signal, the circuit device can reduce low-frequency noise, such as 1/f noise, generated within the signal band, compared to the related art in which an analog circuit performs a bandpass filter process or a demodulation process. Therefore, this circuit device can provide a low-noise physical quantity detection signal.

In the circuit device according to the first aspect, the demodulation circuit may include a mixing circuit that uses the digital signal output from the analog-to-digital conversion circuit as a detected signal to mix the detected signal with the detection signal.

A second aspect of the present disclosure is a circuit device connected to a physical quantity detection element that has a driver and a detector. The circuit device includes a drive circuit that drives the driver and that generates a periodic signal, based on a signal output from the driver; a detection circuit that generates a physical quantity detection signal related to a physical quantity detected by the detector, based on a signal output from the detector. The detection circuit includes an analog front end that amplifies the signal output from the detector; an analog-to-digital conversion circuit that converts a signal output from the analog front end into a digital signal; a bandpass filter circuit that receives the digital signal output from the analog-to-digital conversion circuit; and a demodulation circuit that uses the periodic signal as a detection signal to demodulate a physical quantity signal contained in a signal output from the bandpass filter circuit, based on the detection signal. The detection circuit generates the physical quantity detection signal, based on the demodulated physical quantity signal.

A circuit device, as described above, includes a bandpass filter circuit that outputs a signal obtained by sufficiently attenuating high-frequency noise contained in a digital signal output from an analog-to-digital conversion circuit. Thus, when demodulating a physical quantity signal based on the detection signal, a demodulation circuit can suppress high-frequency noise generated by harmonics contained in the detection signal from being folded back into the signal band. Furthermore, being formed as a digital circuit, the bandpass filter circuit does not involve a large circuit area and a large amount of power consumption, compared to a case where the bandpass filter circuit is formed as an analog circuit. Therefore, this circuit device can provide a low-noise physical quantity detection signal with a small scale of circuitry therein.

Using a digital circuit to perform a bandpass filter process and a process of demodulating the physical quantity signal, the circuit device can reduce low-frequency noise, such as 1/f noise, generated within the signal band, compared to the related art in which an analog circuit performs a bandpass filter process or a demodulation process. Therefore, this circuit device can provide a low-noise physical quantity detection signal.

In the second aspect of the circuit device, the demodulation circuit may include a mixing circuit that uses the signal output from the bandpass filter circuit as a detected signal to mix the detected signal with the detection signal.

In the second aspect, the circuit device may further include a center frequency control circuit that controls a center frequency of the bandpass filter circuit, based on a difference in phase between the periodic signal and the detection signal.

A circuit device, as described above, can provide the detection signal synchronized with the periodic signal, even if a periodic signal based on a signal output from the driver is asynchronous to a clock signal for which the bandpass filter circuit generates the detection signal. Therefore, this circuit device can detect a physical quantity with great precision because the demodulation circuit precisely demodulates the physical quantity signal.

In the second aspect of the circuit device, the analog-to-digital conversion circuit may be a delta-sigma analog-to-digital conversion circuit.

In a circuit device, as described above, an analog-to-digital conversion circuit reduces noise within the signal band which is contained in a digital signal output from an analog-to-digital conversion circuit, because of the noise-shaping effect of a delta-sigma analog-to-digital conversion circuit. Furthermore, this circuit device uses a 1-bit signal as the digital signal output from the analog-to-digital conversion circuit. It is thus possible to realize a compact demodulation circuit with a simple configuration.

According to a third aspect is a physical quantity detection device that includes an aspect of the circuit device and the physical quantity detection element.

A physical quantity detection device, as described above, includes a circuit device in which a bandpass filter circuit outputs a detection signal obtained by sufficiently attenuating harmonics contained in a periodic signal or outputs a signal obtained by sufficiently attenuating high-frequency noise contained in a digital signal output from an analog-to-digital conversion circuit. It is thus possible to suppress high-frequency noise generated by harmonics contained in the detection signal from being folded back into a signal band when the demodulation circuit demodulates a physical quantity signal based on a detection signal. Furthermore, being formed as a digital circuit, the bandpass filter circuit does not involve a large circuit area and a large amount of power consumption, compared to a case where the bandpass filter circuit is formed as an analog circuit. Therefore, this physical quantity detection device can provide a low-noise physical quantity detection signal with a small scale of circuitry in the circuit device.

In a physical quantity detection device, as described above, a circuit device uses a digital circuit to perform a bandpass filter process and a process of demodulating the physical quantity signal. Thus, the circuit device can reduce low-frequency noise, such as 1/f noise, generated within the signal band, compared to the related art in which an analog circuit performs a bandpass filter process or a demodulation process. Therefore, this physical quantity detection device can provide a low-noise physical quantity detection signal.